Nitrate methemoglobinemia

Nitrate and Nitrite. Nitrate is usually present in trace quantities in surface waters but occasionally occurs in high concentrations in some groundwaters. If present in excessive amounts, it can contribute to the illness infant methemoglobinemia. Nitrate is an essential nutrient for many photosynthetic autotrophs. Nitrite is an intermediate in the reduction of nitrate as well as in the oxidation of ammonia it is also used as a corrosion inhibitor in some industrial processes. 

NaNC>3 excess Central Asia deserts Excess of nitrates in forages Endemic methemoglobinemia... 

In 1945, H. H. Comly first estimated the correlation between nitrates in drinking water and the incidence of methemoglobinemia. Research shortly afterwards showed that no cases of methemoglobinemia had been reported in any area of the United States where the water supply contained less than 45 ppm of nitrate ion. This value has become accepted in USA as the upper limit for the nitrate concentration in drinking water. At present the WHO limit is also 45 ppm of nitrate but the value of 22 ppm of nitrate has been set for EC countries. 

As noted under Mechanisms of Toxicity (Section 4.2), nitrate and nitrite esters are vasodilators with resulting hypotension (Nickerson 1975). Therapeutic doses of nitroglycerin for relief of angina are associated with headaches of vascular origin. Both PGDN and the structurally related ethylene glycol dinitrate produce headaches in humans and methemoglobinemia and hypotension in rats (Andersen and Mehl 1979). 

Abortion in pregnant cattle is frequently reported but exact amounts and mechanism of action is not fully understood. The fetus is particularly susceptible to hypoxia induced by the methemoglobinemia. Fetal death and abortion may occur at any stage of pregnancy because of the decreased fetal oxygen and the limited ability of the fetus to metabolize nitrate (Knight and Walter, 2001). 

Donovan JW. 1990. Nitrates, nitrites, and other sources of methemoglobinemia. In LM Haddad and... 

Ellenhorn MJ, Barceloux DG. 1988. Nitrates, nitrites, and methemoglobinemia. In Medical toxicology Diagnosis and treatment of human poisoning. New York, NY Elsevier, 844-851. 

Anesthetized dogs given 50-250mg/kg intravenously immediately showed hypotension, arrest of gut activity, respiratory paralysis, hyperpnea, and moderate methemoglobinemia. Because death was produced with methe-moglobin levels of only 4%, -propyl nitrate intoxication may be caused in part by a direct action on vascular smooth muscle. (It has been noted that the oral toxicity of -propyl nitrate is very low compared with intravenously administered doses, in which mg/kg doses were lethal versus g/kg orally. )... 

Since nitrite ions oxidize the iron atoms of hemoglobin and convert it to methemoglobin, there may be a loss in oxygen delivery to tissues. While methemoglobinemia does not follow therapeutic doses of organic nitrates, it can be observed after overdosage or accidental poisoning. 

Methemoglobinemia is caused by absorbed silver nitrate but occurs rarely... 

Fan, A.M. Steinberg, VE. (1996) Health implications of nitrate and nitrite in drinking water an npdate on methemoglobinemia occnrrence and reprodnctive and developmental toxicity. Regul. Toxicol. Pharmacol, 23, 35-43... 

Some chemicals by their inherent molecular properties possess a high redox potential. o-Aminophenol, for example, is capable of oxidizing ferrohemoglobin to ferrihemoglobin. Nitrates also cause methemoglobinemia. Such one-electron chemical reactions may play a role in mutagenesis. 

Hegesh, E., and Shiloah, J. (1982). Blood nitrates and infantile methemoglobinemia. Clin. Chim. Acta 125, 107-115. 

The gut bacteria may also reduce nitrates to nitrites, which can cause methemoglobinemia or may react with secondary amines in the acidic environment of the gut, giving rise to carcinogenic nitrosamines. 

Numerous substances detected in drinking waters are known to induce toxicity but usually at dose levels much higher than those found in water. Nitrates or nitrites can cause infant methemoglobinemia, lead can affect the hematopoetic or nervous system, cadmium can cause renal damage, and some organohalogens may cause liver toxicity (12). 

Strauch B, Buch W, Grey W, et al. 1969. Methemoglobinemia A complication of silver nitrate therapy used in burns. AORN Journal 10 54-56. 

Nitrate, which is produced by oxidation of nitrogen, is a monovalent polyanion having the formula N03. Most metal nitrates are soluble in water and occur in trace amounts in surface- and groundwaters. Nitrate is toxic to human health and, chronic exposure to high concentrations of nitrate, may cause methemoglobinemia. Maximum contaminant limit in potable water imposed by U.S. EPA is 10 mg nitrate as nitrogen/L. 

Nitrate accumulation may occur in plants growing on soil fertilized with nitrate under moisture-deficient conditions. In the stomachs of ruminant animals, nitrate (NOj) ingested with plant material is reduced to nitrite (N02). The nitrite product enters the bloodstream and oxidizes the iron(II) in hemoglobin to iron(III). The condition that results is methemoglobinemia, which was discussed in Section 15.3 in connection with aniline poisoning. 

Nitrate buildup inducing eutrophication in the receiving bodies of water and/or methemoglobinemia (lack of oxygen in infants)... 

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